As is well known, manufacturing integrated circuits (“ICs”) on substrates such as, for example, and without limitation, semiconductor wafers or glass substrates, requires carrying out many different processing steps in many different semiconductor manufacturing tools, each of which semiconductor manufacturing tools includes a transfer chamber and one or more processing chambers.
A wide variety of gases are used to manufacture the ICs, which gases include, without limitation, inert gases such as, for example, and without limitation, helium, and toxic and/or corrosive gases such as, for example, and without limitation, chlorine. In order to manufacture such ICs properly, the gases must be delivered to the processing chambers in precise amounts. As is well known, a typical semiconductor manufacturing tool utilizes one or more chemical delivery systems to deliver one or more chemicals in gaseous form to various ones of the processing chambers.
As is known, such a chemical delivery system (often referred to in the art as a “gas panel”) is typically divided into a number of gas transmission units (one for each gas being used), which gas transmission units are often referred to in the art as “gas sticks.” FIG. 1 shows a pictorial representation of typical gas stick 100. In a typical gas panel, signals output from one or more components of gas stick 100 are applied as input to chamber control module 200 (“CCM 200”), which CCM 200 typically includes a central processing unit (“CPU”) (not shown). The signals output from the one or more components of gas stick 100 may be in analog or digital form, and in any case, the signals are typically converted into a standard digital protocol such as, for example, and without limitation, the well known “device net” protocol. In a typical case conversion from an analog signal to a digital signal for a particular component is performed on an electronic board associated with the particular component. Then, the CPU in CCM 200, in response to the signals, executes algorithms using predetermined ones of the signals, and applies results therefrom in the form of output signals to semiconductor manufacturing tool controller 300 that is associated with the semiconductor manufacturing tool in a well known manner.
As shown in FIG. 1, gas stick 100 includes manual valve 110. Gas enters gas stick 100 through manual valve 110 at pressures in a range, for example, and without limitation, from about 30 psia to about 45 psia. As is well known, manual valve 110 is utilized to enable manual shut-down of gas stick 100 for safety reasons and for maintenance. Next, the gas passes through pressure regulator 120 and pressure transducer 130 where it exits at a pressure, for example, and without limitation, of about 30 psia. As is well known, because a typical mass flow controller (“MFC”) is susceptible to error caused by changes in inlet pressure (for example, MFC 160 in gas stick 100), pressure regulator 120 is used to protect the MFC (for example, MFC 160) from errors that might be caused by sudden changes in inlet pressure. As is well known, pressure transducer 130, located just downstream of pressure regulator 120 in FIG. 1, is used to measure a gas pressure output from pressure regulator 120, and to provide that measurement as an output signal to CCM 200. The pressure measured by pressure transducer 130 is taken to be equal to an inlet gas pressure to MFC 160. As is well known, in accordance with prior art techniques, the output signal from pressure transducer 130 is used for setup of, and for performing maintenance on, gas stick 100.
Next, the gas passes through filter 140, pneumatic valve 150, MFC 160, and finally through pneumatic valve 170 into a processing chamber on the semiconductor manufacturing tool at a processing pressure (for example, and without limitation, in one typical etch application the processing pressure may be about 100 mT). As is well known, filter 140 serves, for example, to remove particles generated in pressure regulator 120, and pneumatic valves 150 and 170 are used for well known control purposes (pneumatic valves 150 and 170 are typically shut when a processing step is not running in the processing chamber).
As is well known, MFC 160 is used to measure and control precisely the gas flow (for example, in units of mass per unit time) being delivered to the processing chamber. A typical MFC has a maximum gas flow, i.e., a full scale gas flow (“F.S.”), and typically can control gas flow to any value, typically referred to as a Set Point (“S.P.”), in a range between about 10% and about 100% of F.S. to an accuracy of about ±1% of F.S. within ≦about two (2) seconds. A typical MFC produces an output signal that is applied as input to CCM 200 in digital form to provide a measure of gas flow output thereby.
Lastly, as is well known, the above-described components of gas stick 100 are typically mounted on a panel that is often referred to in the art as a substrate.
In accordance with prior art methods, stable flow in gas stick 100 is determined by utilizing the output signal provided by MFC 160 to CCM 200. In particular, in accordance with such prior art methods, once the MFC output signal is within about ±1% of F.S., it is assumed that gas flow in gas stick 100 is stable. In accordance with such prior art methods, since stabilization of the MFC output signal typically occurs within about two (2) seconds, gas flow stabilization is typically deemed to have occurred within about two (2) seconds.
The inventors have discovered that, in practice, gas flow stabilization in a gas stick may take much longer than two (2) seconds. In addition, the inventors have discovered that the amount of time for gas flow to stabilize may depend on the particular gas in the gas stick, and that it may even depend on the age of the gas stick itself. However, if one were to utilize an arbitrarily long stabilization period of, say, ten (10) seconds to overcome this problem, throughput (when measured, for example, as a number of wafers processed per hour) might be negatively impacted since processing would be halted during this long stabilization period. In addition, if such an arbitrarily long stabilization period were still smaller than the amount of time it takes for the gas flow to stabilize, the amount of gas entering the processing chamber may not be the desired amount. This would be problematic for critical processes where the yield per process run (when measured, for example, as the number of properly functioning devices on the substrate) might be negatively impacted.
In light of the above, there is a need for method and apparatus that analyzes gas flow in a gas stick to solve one or more of the above-identified problems.